Exhaust system for a diesel engine

ABSTRACT

An exhaust gas system for a diesel engine comprises a filter  9  that includes channels extending in the direction of flow and having porous walls  13  which are clad with an SCR catalyst coating  25.  Neighbouring channels are alternately shut off by end plugs  15, 17  at the inlet end and the outlet end, as a result of which the exhaust gas is forced to flow through the walls. 
     The walls  13  are coated with an AMOX catalyst coating  29  from the end  21  over a distance  27.  The end plugs  17  in the outlet ends have a length that at least equals said distance  27.  As a result, one side of the wall sections coated with the AMOX catalyst coating is covered and the exhaust gas cannot but flow first through the wall sections coated with SCR catalyst coating  25  and only then can the exhaust gas flow past the wall sections coated with the AMOX catalyst coating  29.

FIELD OF THE INVENTION

The invention relates to an exhaust gas system for a diesel enginecomprising an inlet and an outlet and a filter located in betweencomprising a plurality of channels arranged next to one another andhaving porous walls, where neighbouring channels are alternately shutoff by an end plug at the inlet end and the outlet end, as a result ofwhich the exhaust gas is forced to flow through the walls which are atleast partially coated with a first coating.

STATE OF THE ART

An exhaust system of this type is generally known in the form of adiesel particle filter (DPF) in which the walls of the channels arecoated with a selective catalytic reduction catalyst (SCR catalyst). Theend plugs are generally installed before the walls are coated.

Once the exhaust gas has flown through the DFP with the SCR catalyst onit, it is desirable to have the filtered exhaust gas flow past anammonia oxidation catalyst (AMOX catalyst).

SUMMARY OF THE INVENTION

It is an object of the invention to provide an exhaust gas system of thetype defined in the opening paragraph which is advantageously providedwith an AMOX catalyst. For this purpose the exhaust gas system accordingto the invention is characterized in that from the outlet end to adistance from this outlet end, the walls are coated with a secondcoating, where the end plugs in the outlet ends have a length that is atleast equal to said distance over which the walls are coated with thesecond coating. If the AMOX catalyst has not been coated in the place ofthe end plugs on the walls of the channels, the exhaust gas willpartially flow through the AMOX catalyst coated wall sections andpartially through the SCR catalyst coated wall sections. By covering oneside of the sections of the walls which are coated with the AMOXcatalyst, the exhaust gas cannot but flow first through the SCR catalystcoated sections of the walls. Not until then can the exhaust gas flowpast the wall sections coated with the AMOX catalyst coating. Byshutting off the wall sections coated with the AMOX catalyst coating bymeans of the end plugs, no extra closing means are required. Only theend plugs in the outlet end need to be made longer than normal.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention will be further described below in more detail withreference to an embodiment of the exhaust gas system according to theinvention represented in the drawing figures, in which:

FIG. 1 shows an embodiment of the exhaust gas system according to theinvention in longitudinal section; and

FIG. 2 gives a detailed representation of the interior of the exhaustgas system shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 shows an embodiment of the exhaust gas system for a diesel engineaccording to the invention. The exhaust gas system 1 comprises a housing3 which has an inlet 5 and an outlet 7 and a filter 9 accommodated inthe housing. The filter comprises channels 11A and 11B extending in thedirection of flow and having porous walls 13. The channels are open atone end and closed at the other by means of an end plug 15, 17. Thechannels 11A open at the inlet end 19 and closed at the outlet end 21are then surrounded by channels 19B open at the outlet end 21 and closedat the inlet end 19. As a result, the exhaust gas 19 is forced to flowthrough the walls 13.

FIG. 2 gives a detailed representation of the interior of the filter 9in enlarged form. From the inlet end 19 onwards the walls 13 are coatedwith an SCR coating 25 over a first distance and coated with an AMOXcatalyst coating 29 from the outlet end 21 onwards over a seconddistance 27. The end plugs 17 in the outlet ends have a length that atleast equals said second distance 27 over which the walls are coatedwith the AMOX catalyst coating 29. As a result, one side of the wallsections coated with the AMOX catalyst coating is covered and theexhaust gas cannot but flow first through the wall sections 13 coatedwith SCR catalyst coating 25. Only then can the exhaust gas flow pastthe wall sections 13 coated with the AMOX catalyst coating 29.

Albeit the invention has been elucidated in the foregoing with referenceto the drawing figures, it should be set out that the invention is notby any manner or means restricted to the embodiments shown in thedrawing figures. The invention also extends to any embodiments deviatingfrom the embodiments shown in the drawing figures within the spirit andscope defined by the claims.

1. An exhaust gas system for a diesel engine comprising an inlet and anoutlet and a filter located in between comprising a plurality ofchannels arranged next to one another and having porous walls, whereneighbouring channels are alternately shut off by an end plug at theinlet end and the outlet end, as a result of which the exhaust gas isforced to flow through the walls which are at least partially coatedwith a first coating, characterized in that from the outlet end to adistance from this outlet end, the walls are coated with a secondcoating, where the end plugs in the outlet ends have a length that is atleast equal to said distance over which the walls are coated with thesecond coating.
 2. An exhaust gas system as claimed in claim 1,characterized in that the filter is a diesel particle filter, in thatthe first coating is a selective catalytic reduction coating and in thatthe second coating is an ammonia oxidation catalyst coating.